This software is still in development, so we don’t recommend you run it on a production site. Consider setting up a test site just to play with the new version. To test WordPress 4.0, try the WordPress Beta Tester plugin (you’ll want “bleeding edge nightlies”). Or you can download the beta here (zip).

4.0 is due out next month, but to get there, we need your help testing what we’ve been working on:

Previews of embedding via URLs in the visual editor and the “Insert from URL” tab in the media modal. Try pasting a URL (such as a WordPress.tv or YouTube video) onto its own line in the visual editor. (#28195, #15490)

The Media Library now has a “grid” view in addition to the existing list view. Clicking on an item takes you into a modal where you can see a larger preview and edit information about that attachment, and you can navigate between items right from the modal without closing it. (#24716)

We’re freshening up the plugin install experience. You’ll see some early visual changes as well as more information when searching for plugins and viewing details. (#28785, #27440)

The editor intelligently resizes and its top and bottom bars pin when needed. Browsers don’t like to agree on where to put things like cursors, so if you find a bug here, please also let us know your browser and operating system. (#28328)

We’ve made some improvements to how your keyboard and cursor interact with TinyMCE views such as the gallery preview. Much like the editor resizing and scrolling improvements, knowing about your setup is particularly important for bug reports here. (#28595)

Widgets in the Customizer are now loaded in a separate panel. (#27406)

We’ve also made some changes to some formatting functions, so if you see quotes curling in the wrong direction, please file a bug report.